Seasonal Variations of Phytoplankton Production in an Estuary in Relation to Coastal Water Movements

Abstract

Primary production and phytoplankton biomass in Port Hacking, an estuary 24 km south of Sydney, were measured at 2-4 day intervals for one year. Primary production was measured by in situ ¹⁴C uptake, and phytoplankton biomass by ¹⁴C uptake at constant irradiance and in vivo chlorophyll fluorescence. Measurements of solar irradiance and light attenuation by the water column were also obtained. Nutrient concentrations were measured both in the estuary and in the coastal waters adjacent to Port Hacking.

The short-term variations of phytoplankton biomass were found to be due to both estuarine hydrological events resulting in the release of regenerated nutrients, and to coastal hydrological events, where slope water intrusions enriched the coastal waters and were introduced into the estuarine basins by tidal exchange.

The annual variation of primary production in Port Hacking was related to the annual variation of solar irradiance. A minor part of the annual variation appeared to be due to temperature, but the nature of this relationship was uncertain.